Stability of Crown Pillar during Transition from Open Pit to Underground Mining

Abstract

Mineral deposits at shallow depth are on the verge of exhaustion and transiting to underground mining operations, for extraction of deposits at depth has now become inevitable. The depth of open pit mine is generally governed by the stripping ratio and lateral extent of lease. When open pit reaches its ultimate designed depth and the ore is still existing at greater depth transition is must and barrier pillar needs to be left in between both the workings. If underground mining is below an opencast mine then stability of barrier/crown pillar between open pit and underground mining becomes critical especially when non-caving method is to be followed. It has its own implications and maintaining safety of pit and slope along with underground workings becomes a real challenge. Ground monitoring in terms of induced stresses and displacement holds paramount importance. The most popular method in metal mining is Long Hole/Blast Hole Stoping Method in top down sequence. Earlier hydraulic fill was common and is now being slowly replaced by Paste fill. In this chapter a few challenges existing in Indian mining scenario is discussed along with review of methodologies for optimum design of crown pillar. Parameter influence is also explored for its stability.